Method and apparatus for variable pitch propellers

ABSTRACT

THE LOAD ON THE ENGINE OF A SHIP IS MAINTAINED WITHIN PRESCRIBED LIMITS BY MAKING AN ADJUSTMENT OF THE PROPELLER OF THE SHIP TO COMPENSATE FOR CHANGES IN WIND AND SEA CONDITIONS AND THE LIKE. THIS IS ACCOMPLISHED BY GENERATING A CORRECTIVE SIGNAL, DEPENDING ON THE DISCREPANCY THAT MAY EXIST BETWEEN ACTUAL AND DESIRED ENGINE LOAD. THE CORRECTIVE SIGNAL, IN THE FORM OF A TRAIN OF PULSES, CONTROLS A SERVOMECHANISM THAT ADJUSTS PROPELLER PITCH.

lnventors Carl-AxelLlndahl Krlstinehamn; Bengt Ludvig Ohlsen; Lars Ake Valdemar lljort, Nynashamn, Sweden Appl. No. 851,339 Filed Aug. 19, 1969 Patented June 28, 1971 Assignee Aktiebolaget Karlstads Mekaniska Werkstad Karlstad, Sweden Priority Aug. 21, 1968 Sweden 1 1231/68 METHOD AND APPARATUS FOR VARIABLE PITCH PROPELLERS [50] Field ofSearch 4l6/l,27, 30, 25, 26, 28, 29

[56] References Cited UNITED STATES PATENTS 2,155,586 4/1939 Ebert 416/30 3,088,523 5/1963 Smaller 416/1 3,089,548 5/1963 Klaassen..... 416/30 3,110,348 12/1963 Greiner 416/27 3,302,724 2/1967 Brooks 416/27 3,386,516 6/1968 Nitzki 416/1 Primary Examiner-Clarence R. Gordon Attorney Brumbaugh, Graves, Donohue & Raymond ABSTRACT: The load on the engine of a ship is maintained within prescribed limits by making an adjustment of the propeller of the ship to compensate for changes in wind and sea conditions and the like. This is accomplished by generatls Claims 4 Drawing ing a corrective signal, depending on the discrepancy that may 11.8. CI 416/1, exist between actual and desired engine load. The corrective 416/27, 416/30 signal, in the form of a train of pulses, controls a ser- Int. Cl B63h 3/10 vomechanism that adjusts propeller pitch.

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CARL-AXEL LINDAHL1 BENG'I' LUDVIG OHLSEN 8x LARS AKE VALDEMAR HJORT M43 4. IQM? their ATTORNEYS PATENTEU JUH28 19?:

ENGINE LOAD SHEET UF 4 FUEL PUMP posmo M/VENTO/PS. CARL-AXEL LINDAHL- BENGT LUDVIG OHLSEN 8| LARS AKE VALDEMAR HJORT their ATTORNEYS METHOD AND APPARATUS FOR VARIABLE PITCH PROPELLERS BACKGROUND OF THE INVENTION This invention relates to load control and, more particularly, to novel and highly effective methods and apparatus facilitating control of the load on the engine or engines of a ship having one or more variable-pitch propellers. In still greater detail, the invention relates to methods and apparatus whereby engine speed is maintained at any desired value by adjusting the fuel supply to the engine to produce a desired engine load, sensing the fuel pump position, and comparing the fuel pump position to preset limit values, in such a manner that, upon exceeding of these limit values, a corrective signal is generated and supplied to a servosystem for so changing the pitch of the propeller blades that the load on the engine reassumes its desired value.

In the design and construction of conventional load-control devices, the stroke of the fuel pump is generally regarded as representative of the load on the engine and is utilized as an input value to the load-control devices. Other parameters for the engine load, for example exhaust gas temperature, number of revolutions of turbosupercharger per unit of time, etc., can also be utilized as a measure of the engine load.

One conventional load-control device includes a hydraulic, pneumatic or electric signal generator that receives an input from the control rod of the fuel pump. The signal generator generates a signal that is used for so correcting the propeller pitch that the desired engine load is obtained. Control devices of certain types are provided with a built-in hydraulic loadcontrol valve controlling a servomotor, which in its turn in a suitable way corrects the propeller pitch and thereby the engine load. The relation between the number of engine revolutions per unit of time and the fuel pump stroke is established by a cam, which represents the rated or desired number of revolutions. The engine, therefore, can be overloaded if the external load reduces the number of engine revolutions per unit oftime to a value below the rated value. There exist constructions basing the permissible engine load on the actual number of engine revolutions per unit of time, but these constructions are mechanically complicated. One complicated remote-control device involves two load levels. The load level can also be adjusted by a screw. However, there exist no simple constructions for continuous, automatic, remote control of the load level.

In conventional systems, sensitivity cannot be adjusted other than by exchanging the control valve. Moreover, conventional load-control devices tend to be unstable, among other reasons because the construction comprises several servosystems. Thus, the signal from a load-control device cor rects the setting of a servomotor which in turn corrects a servomotor in the propeller hub.

SUMMARY OF THE INVENTION An object of the invention is to remedy the shortcomings of conventional methods and apparatus noted above. In particular, an object of the invention is to provide simple and efficient methods and apparatus facilitating continuous, automatic, remote control of the engine load in such a manner as to maintain engine load at an optimum level.

The foregoing and other objected of the invention are at tained, in a representative embodiment thereof, by sensing fuel-pump position, comparing the sensed position to preset limit values, generating a corrective signal upon exceeding of the limit values, and supplying the corrective signal to a servosystem for so adjusting the ship propeller blade pitch that engine load reassumes its desired value. In accordance with the invention, the corrective signal is converted into a pulse train that is supplied to the servosystem, so that the adjustment of propeller pitch is stepwise, one step corresponding to each pulse in the pulse train. Stability ofoperation is obtained, and load variations of short duration do not affect the propeller pitch. The time for a load change to affect the pitch is adjustable. The load level of the engine, furthermore, is adjustable continuously so that there is, for example, the possibility of slowly increasing the engine load during the heatingup period of the engine. Overload of the engine because of failure of agreement between the number of engine revolutions per unit of time and the setting of the fuel pump is impossible, because the actual number of revolutions of the engine is the reference value for the engine load.

BRIEF DESCRIPTION OF THE DRAWING An understanding of additional aspects of the invention can be gained from a consideration of the following detailed description of two representative embodiments thereof, in conjunction with the appended FIGS. of the drawings, wherein:

FIG. 1 is a schematic representation ofa first representative embodiment of apparatus constructed in accordance with the invention;

FIG. 2 is a schematic representation ofa portion of the apparatus of FIG. 1;

FIG. 3 is a schematic representation of a second embodiment of apparatus constructed in accordance with the invention; and

FIG. 4 is a graph of a representative actual load curve and limit load curves generated by the apparatus of FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENT It is within the scope of the invention to employ any of a number of parameters as representative of engine load, as indicated above. In the preferred embodiments, the fuel-pump position is taken as a measure of the engine load, and this therefore is sensed by a position transducer. In multi-engine installations there is a transducer for each engine. Signals from the transducer are compared to a reference value corresponding to predetermined maximum and minimum permissible loads for the engine in question at the engine speed in question. At overload a downwardly adjusting impulse to the pitch is obtained, and at underload an upwardly adjusting impulse. The impulse does not directly affect the main servo, but

only the return circuit therefor, thereby ensuring safety of operation. For ensuring stability of operation, the pulse duration and the pulse frequency are adjustable, and so is the time of initiation of the first pulse. It may be expressed in this way: The equipment has time to respond to one pulse before a further pulse is emitted.

In multi-engine installations where there can be simultaneously an indication of overload as to one engine and underload as to another, the signal that indicates overload takes precedence. By introducing a suitable time for initiation of the first corrective pulse, the apparatus of the invention does not affect the propeller pitch in response to disturbances of short duration, but upon a change of the average load (caused, for example, by headwind or tailwind) of sufficient duration, a suitable adjustment of the pitch takes place. Since the correction of the pitch is stepwise and quantitatively limited, a catastrophic adjustment cannot occur under any circumstances. By means of a switch Manual/Automatic" the automatic system can be connected or disconnected, and in the Manual position the pitch can be finely adjusted by pushbuttons from the bridge.

In order to obtain a reliable system that is adapted for use with conventional equipment, an electrohydraulic system is employed that comprises semiconductor components from the signal emitters to the control means for the hydraulic system. At a correct setting of the equipment, the fuel pump position (representative ofengine load) thus is always within a set range for full load, with the exception of the short periods within which the automatic system is not given sufficient time of action, for example at too rapid actuation of full speed ahead" or at strong head-sea. In the case of small increments of load change, however, the automatic system so adjusts the pitch that the engines operate with full load irrespective of increasing or decreasing resistance: i.e., an optimum utilization of resources is obtained which results in highest possible speed without continuous overload. It is presupposed hereby that the shaft generator is engaged, so that the number of revolutions of the engines per unit of time is constant. If the automatic system is intentionally or unintentionally deactivated, the pitch can easily be adjusted manually from the bridge or another convenient location. By maintaining, for example, the pushbutton for Decrease" depressed for period of different length, a greater or a smaller step ofthe pitch correction is obtained. I

FIG. 1 shows an engine installation comprising two main engines l and 2. The engines 1 and 2 drive via a reduction gear 3 a single propeller 4 the pitch of which is adjustable by an adjusting device 5 operated by a servosystem 6. It is within the scope of the invention to employ a single engine to drive the propeller 4 and alternatively to employ, for example, a separate engine-reduction gear combination to power each of a plurality of propellers. Signals for adjusting the propeller 4 for ahead or astern motion arrive through a direct line 7 from a control 7 mounted in the control room of the ship. A line 8 is the return circuit for the pitch adjustment of the propeller. In the line 8 is placed an analog-to-digital signal converter 9 from which pulses are directed to the servosystem 6. The signal converter 9 converts analog signals from a signal selec tor 10 into pulses. The pulses are supplied to the servosystem 6 and are converted by relay and solenoid valve into control impulses for the servosystem 6. The control impulses correspond directly to the impulses emitted by the signal converter 9. The signal selector 10 receives an input from sensors 11 and 11 operatively associated with the engines l and 2, respectively. Thesensors 11, and 11 record or sense the positions of the fuel pumps for the engines 1 and 2 and thereby the loads of the engines I and 2, respectively. The sensors ll and 11, emit signals at overload and underload, as the case may be. Each of the sensors 11, and 11 may comprise, for exam ple, two limit position switches which are connected at a certain position of the fuel pump setting. Each of the sensors I1, and ll alternatively may comprise one limit position switch which permanently emits a signal, the nature of which is determined by the position of the fuel pump. Such signal is compared in the sensor 11 or 11 as the case may be, and from the sensor lll or 11 are transmitted only signals of a certain nature, for example signals indicative of the exceeding of a certain position of the fuel pump setting.

Preferably, at a certain position of the fuel pump setting, which, for example, represents an overload of. considerable size, in which case a rapid downward adjustment of the propeller pitch is desired, a signal generated by the sensor 11, or 11 is fed directly to the servosystem 6 via the signal selector l0 and a line 12, thus bypassing the signal converter 9. Thereby the initial adjustment of the propeller pitch is not made by steps, but such stepwise adjustment takes place after the elimination of the large overload. When each of the sensors II and 11 comprises two limit position switches that limit the range of the fuel pump within which no propeller adjustment takes place, the effect described immediately above is achieved by providing at least one additional limit position switch outside said setting range. Signals generated upon closing of this switch are supplied through the line line 12 (bypassing the signal converter 9) and to the servosystem 6, which adjusts the pitch. When each of the sensors 11 and 11 comprises a position converter, the converter has a comparator which allows the passage ofa signal ofa certain nature corresponding, for example, to a high setting of the fuel pump. Such signal goes past the signal converter 9 through the line 12, as in the previous example.

FIG. 2 shows the servosystem 6 and associated apparatus in greater detail. The components 9-11 described above are connected in the normal control system for pitch adjustment. A desired rated value of the pitch always is set by a control C and transmitted in the form of, for example, a pneumatic signal through lines 210 and 21b to an auxiliary servomotor 2]. The auxiliary servomotor 21 includes a stationary cylinder 21c within which a piston 21d is slidable. The piston 21d is connected by a connecting rod 212 to an adjusting crank 22 which through a valve rod 23 actuates a hub servomotor 24. The servomotor 24 adjusts the pitch of the blades of the propeller 4 in a way that corresponds exactly to the position of the auxiliary servomotor piston 211d. The auxiliary servomotor 2i is provided with a feedback loop comprising a servomotor 25, feedback links 26 and 27, and a valve 28. The servomotor 25 is controlled by the control device via a solenoid valve 29. The servomotor 25 includes a stationary cylinder 25a within which a piston 25b is slidable. Fluid lines 25c and 25d extend from the valve 29 to opposite ends of the cylinder 25a. The piston 25b is connected by a connecting rod 25e to the link 26. The control device, by the servomotor 25, can vary the feedback ofthe auxiliary servomotor 21 and thereby vary the pitch ofthe propeller 4 about the rated value set.

As FIG. 2 shows, the maximum possible change of pitch depends on the position of the adjustment crank 22. The pitch, for example, cannot be changed at all by the servomotor 25 when the crank 22 is in resting position representing zero pitch.

Another embodiment of the apparatus of the invention is shown in FIG. 3. In this embodiment the electronic system, where possible, is built up of integrated circuits. The logical circuits are of high-level type with an insensitiveness to disturbances of 3 v., and the counters are of low-level type. Input signals in the form of an alternating voltage come from a tachometer generator 31. Other input signals in the form of a direct voltage come from the position sensors of the fuel pumps (0 to 10 v.) and are led each via potentiometers 32, 33 to a signal selector 34. In brief outline, the signals are treated as follows: A load curve (FIG. 4) is generated in a function generator 36, and the highest fuel pump position (FPP) is sensed in the signal selector 34. FIG. 4 includes a curve 36a representing actual engine load as a function of fuel pump position, a curve 3611 representing maximum permissible load, and a curve 360 representing minimum permissible load. Comparison is made in a summator 37 between the desired value of the fuel pump position and the highest real value. The difference obtained in the summator 37 is compared to the limits of overload and underload. Upon exceeding said limits, after a certain delay a pulse train is started which is produced by a pulse generator 38. A possible pulse train from the pulse generator 38 to any of the solenoid valves 35 so adjusts the pitch that the load is caused to be again within the permissible limits, provided that they are within the control range.

The signal treatment in greater detail is as follows. The tachometer voltage from the generator 31 is rectified in a rectifier 39 and thereafter controls the function generator 36. The generator 36, the active elements of which are two operation amplifiers, generates a function which by four straight lines approximates the load curve in question. The function is determined by the setting of a number of potentiometers. The output voltage of the generator (0 to +10 v.), thus, at every moment is a measure of the highest permissible fuel pump position. By a potentiometer 40 connected to receive as its input the output of the function generator, the load curve can be displaced downwardly to the desired rated value of the fuel pump position. This is represented by the expression ouf nomr where U is the output of the potentiometer 40, FPP,,,,,,, is the desired rated value of the fuel pump position, and K is a constant. The position sensors of the fuel pumps are connected through the potentiometer 32, 33 to the signal selector 34, which allows the passage of the greatest (most negative) input signal. The output voltage of the signal selector 34 indicates the highest actual value of FPP, but with a negative sign, This is represented by the expression ouF nrt mar K where U is the output of the signal selector 34 and FPP is the actual maximum fuel pump position. The selector 34 comprises m silicon diodes d where m number of engines.

The output voltages from the signal selector 34 and from the potentiometer 40 are added in a sign-reversing summator 37. The active element is an operation amplifier. The output voltage from the summator 37 then is a measure of the dif ference FPP ,,,,,FPP,,,, The summator 37 is connected to two comparators 41 and 42. When the difference FPP ,,,,,,.FPP,,,,,, exceeds a certain value, the output voltage of one ofthe comparators changes from 0 v. to v. and thereby indicates overload. lf the difference is negative and exceeds a certain value, the output voltage of the other comparator changes to +10 v. and thereby indicates underload.

The comparators 41 and 42 are connected to a logic system that functions as follows. The signals from the comparators 41 and 42 are stopped when the number of engine revolutions per unit of time in question is lower than a predetermined value (the no-load number of revolutions per unit of time). This is realized by means of AND circuits 43, 44 and by a third comparator 45 sensing the number of engine revolutions per unit of time. When the number of engine revolutions per unit of time exceeds the no-load number of revolutions and an overload or underload signal is emitted from the comparators 41 or 42, a signal is sent to the pulse generator 38 via a delay circuit therein and an OR circuit 46.

After an adjustable delay to prevent response to transient phenomena the pulse generator 38 commences the sending of a pulse train with adjustable pulse width and pulse frequency. The pulse train lasts as long as the load is outside of the permissible range. The delay circuit and the pulse generator substantially comprise three counters adapted to be preset.

When a switch Manual/Automatic" 47 is in position "Automatic," as shown, the pulse train is allowed to pass either through the increase-channel or decrease-channel 48 and 49, respectively, depending on whether there is underload or overload, and arrives via an OR circuit 50, 51 (each including an and circuit input) at an amplifier 52, 53. To the OR circuits 50 and 51 further is connected a signal line 54, 55 from a con trol means 56 for manual control of the propeller pitch.

Each of the amplifiers 52, 53 comprises thyristors and closes its relay in timed relationship with the ingoing pulse frequency. The relays of the solenoid valves 35 connect 220 v. alternating voltage to the entry in question of the solenoid (not shown) whereby a pitch change proportional to the total pulse time is obtained.

For operating the governor an operation box is provided on the bridge and an operation board in the control room. On the operation box is mounted the switch 47 for Automatic/Manual" control of the propeller pitch. There are further provided two pushbuttons for themanual control 56. In the buttons are lamps which during automatic operation indicate the corrective pulses in the increase-channel and decrease-channel, respectively, and during manual operation indicate underload and overload, respectively.

On the operation board in the control room there are pro vided four lamps 57, 58. The lamps 57 are connected in parallel with the lamps in the operation box, while the lamps 58 always indicate the corrective pulses. Furthermore, six switches are provided for setting the delay of the pulse generator, the pulse width and the pulse frequency. For potentiometer wheels are provided for setting different reference values for underload, overload and no-load number of revolutions and for lowering the load curve to a suitable nominal value level.

Thus there are provided in accordance with the invention novel and highly effective methods and apparatus facilitating continuous, automatic, remote control of engine load in such a manner as to maintain engine load at an optimum level.

Many modifications of the representative embodiments of the invention described above will readily occur to those skilled in the art. For example, the specified voltages and the details of construction of the various components can be varied within wide limits. The invention is to be construed as including all of the modifications thereof within the scope of the appended claims.

We claim:

1. In a method of load control of ship engines in which engine speed is controlled to be constant by means affecting the fuel supply to the engine, and in which the fuel pump position is sensed and compared to preset limit values in such a manner that, upon exceeding of said limit values, a corrective signal is generated and supplied to a servosystem for so adjusting the pitch of the ship propeller that the load on the engine reassumes the set value, the improvement comprising the steps of converting said corrective signal into a pulse train, supplying said pulse train to said servosystem, and adjusting said pitch in a stepwise manner, one step corresponding to each of said pulses in said pulse train.

2. A method according to claim 1, wherein each pulse in said pulse train is converted into a pneumatic signal for said servosystem.

3. A method according to claim 1, wherein each pulse in said pulse train is converted into a hydraulic signal signal for said servosystem.

4. A method according to claim 1, wherein the length of each of said pulses is adjustable.

5. A method according to claim 1, wherein the time between successive ones of said pulses is adjustable.

6. A method according to claim 1, comprising the step of transmitting said corrective signal to said servosystem directly and without said conversion upon substantial exceeding of said limit values, to effect continuous pitch correction, said conversion of said corrective signal into a pulse train taking place at a closer point to one of said limit values.

7. A method according to claim 1, comprising the step of checking a corrective signal for its duration and, only after a certain adjustable duration, converting said corrective signal into said pulse train.

8. A method according to claim 1, wherein the positions of the limit values are adjustable.

9. A method according to claim 8, wherein the setting of the limit values depends on the permissible range of the engine load.

10. Apparatus for load control of a ship engine driving a variable-pitch propeller, in which, upon the exceeding ofa set limit value, propeller pitch is adjusted to maintain engine load within a predetermined range, comprising means for generating a first signal representative of permissible fuel pump position, means for generating a second signal representative of actual fuel pump position, summator means for combining said first signal representative of permissible fuel pump position and said second signal representative of actual fuel pump position, two comparators responsive to said summator means, one of said comparators generating a signal when said first signal exceeds said second signal by a predetermined amount and the other of said comparators generating a signal when said second signal exceeds said first signal by a predetermined amount, a pulse generator responsive to said comparators for generating a pulse train corresponding to the output of either of said comparators, and two relay means responsive to the output of said pulse generator, one of said relay means being actuated in response to a pulse train corresponding to one of said comparators to decrease propeller pitch and the other of said relay means being actuated in response to a pulse train corresponding to the other of said comparators to in crease propeller pitch.

11. Apparatus according to claim 10, wherein said pulse generator comprises an adjustable delay circuit.

12. Apparatus according to claim 10, wherein said pulse generator is adjustable with respect to pulse width and frequency.

13. Arrangement according to claim 10, comprising a separate AND circuit in series between each of said comparators and said pulse generator and a third comparator sensing the number of engine revolutions per unit of time, said third comparator supplying an input to each of said AND circuits.

14. Apparatus according to claim 10, comprising a potentiometer responsive to said means for generating said first signal for changing the amplitude of said first signal.

15. Apparatus according to claim 10, wherein said means for generating said first signal comprises two operation amplifiers, each generating four straight lines approximating the engine load curve. 

